1. Field of the Invention
The present invention relates to a virtual pilot channel generating apparatus and its operating method for supporting effective hand-off between frequencies in a code division multiple access (CDMA) mobile communications system, specifically, to a virtual pilot channel generating apparatus and its operating method, which periodically sets information determining a CDMA frequency allocation channel in one hardware, to allow one piece of pilot information to be commonly used in a plurality of CDMA frequency allocation channels, thereby effectively supporting hand-off between frequencies.
2. Discussion of Related Art
In general, a base station in a CDMA mobile communications system can use multiple CDMA channels, not being overlapped. The number of CDMA channels used by a specific base station and their frequency bands are determined with regard to a method of allocating frequency for mobile communications and to the estimated number of users in an area where the base station will be established. Accordingly, frequency channels used by base stations located adjacent to the specific base station may be differently allocated.
When a certain user moves from the coverage area of a base station A to the coverage area of a base station B in the aforementioned CDMA mobile communications system, the service provider is changed from the base station A to the base station B, and communication channel is converted from the one used by the user in the base station A to the one available in the base station B. This is called hand-off. Smooth handing-off is an essential element for improving the quality of the mobile communications service. To perform the handing-off, the user""s mobile monitors a pilot channel transmitted from each base station. This is because that the mobile determines the point of time at which the communication channel is changed, that is, a handing-off point, based on the power intensity of the pilot channel received from the two base stations A and B, regarding that the power intensity of the pilot channel received by the mobile is decreased as the mobile becomes more distant from the base station transmission antenna since the pilot channel is transmitted from each base station with an uniform power all the time.
In the above-described method of determining the handing-off point according to the power intensity when a signal is transmitted from each base station to the mobile, there is a problem in the determination of exact handing-off point between base stations which use different frequencies because the amount of reduction in the power of signals transmitted from the base stations to the mobile depends on topography and disturbance element. To solve this problem, there have been continuously studying and developing methods for performing smooth handing-off. One of those is disclosed in U.S. Pat. No. 5,345,467 in which an apparatus for controlling hand-off of radio devices includes first and second matched filters for matching an antenna to a signal output from first and second base stations, first and second detectors for detecting a reception signal and a comparator for comparing the signals received from the two base stations, thereby determining the handing-off point according to the difference in receiving time of the signals received from the two base stations.
This technique can determine the handing-off point more exactly than the aforementioned conventional technique which determines the handing-off point using electric field intensity (power intensity). With the conventional hand-off methods including the technique of U.S. Pat. No. 5,345,467, however, the mobile can search for only one CDMA channel frequency. Thus, when the base stations A and B use different CDMA channel frequencies, it is impossible to monitor the power intensity of the pilot channel of the base station where hand-off will be completed, obstructing the initiation of smooth hand-off between frequencies.
Accordingly, the present invention is directed to a virtual pilot channel generating apparatus and its operating method for supporting effective hand-off between frequencies in a CDMA mobile communications system that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a virtual pilot channel generating apparatus and its operating method for effectively supporting hand-off between frequencies in a CDMA mobile communications system, which periodically sets in the hardware of one base station pilot information which is the same as CDMA allocation frequency used by another base station, that is, information determining CDMA frequency allocation channel, to allow one piece of pilot information to be commonly used by a plurality of CDMA frequency allocation channels, performing effective hand-off between frequencies in the CDMA mobile communications system.
The pilot channel commonly used in the plurality of CDMA frequency allocation channels is called a virtual pilot channel. The virtual pilot channel generating apparatus according to the present invention includes: source supplying means for supplying a source required for generating a virtual pilot channel; a splitter for splitting information on the source provided by the source supplying means into a plurality of signals, the splitter being connected to the signal output port of the source supplying means; and a plurality of signal generating sections for receiving the plurality of signals divided by the splitter and generating different frequency signals, the signal generating sections being connected to the signal output port of the splitter.
In accordance with the present invention, when base stations A and B use frequency channels different from each other and a user moves from the base station A to the base station B, pilot information the same as CDMA allocation frequency used by the base station A is supplied to the hardware of the base station B, to allow one piece of pilot information to be commonly used in a plurality of CDMA allocation frequencies. Furthermore, when the hardware of the base station A transmits the pilot channel the same as the CDMA allocation channel used by the base station B, the user""s mobile can monitor the power intensities of the pilot channels of the two base stations A and B at the same time, resulting in smooth hand-off.
When base stations A and B use frequency channels different from each other and a user moves from the base station A to base station B, pilot information the same as CDMA allocation frequency used in the base station A is supplied to the hardware of the base station B, and the hardware of the base station B transmits a virtual pilot channel identical to CDMA allocation channel used in the base station A, to allow the user""s mobile to simultaneously monitor power intensities of the pilot channels of the base stations A and B, initiating smooth hand-off.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.